Skakeling met diffusie-transistors by höe kollektorspannings word ontleed. Die gebied waar vermenigvuldiging verkry word en skakelsnelheid aansienlik verhoog word, is ondersoek met behulp van 'n relaksasie-ossillator. Lawineskakeling soos veral benut in pulsgenerators, is hier ter sake. Met behulp van 'n ladingsmodel is dit moontlik om uitdrukkings vir stygtyd, piekstroom en daaltyd in terme van transistorparameters te kry. Hierdie waardes is getoets met 2N414-transistors. Die invloed van eksterne komponente en toevoer word beskou. ENGLISH : Switching with transistors (diffusion flow type) in the high voltage region is analysed. The high Switching speed in this multiplication region is investigated by means of a relaxation oscillator. Avalanche mode switching as is relevant here, is mostly used in pulse generators. Expressions for rise time, peak current and fall time are obtained by means of a charge control model in terms of transistor parameters. 2N414 transistors were used to verify the theory experimentally. The influence of external components and supplies are also considered. / Dissertation (MEng)--University of Pretoria, 1969. / Electrical, Electronic and Computer Engineering / unrestricted

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第18991号 / 工博第4033号 / 新制||工||1621(附属図書館) / 31942 / 京都大学大学院工学研究科電気工学専攻 / (主査)教授 引原 隆士, 教授 土居 伸二, 教授 小林 哲生 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

The objective of this dissertation is to develop a mechanical model of a nonlinear piezoelectric energy harvesting system induced by Duffing oscillator and predict the periodic motions of such a nonlinear dynamical system under different excitation frequency. In this dissertation, analytical distributed-parameter electromechanical modeling of a piezoelectric energy harvester will be presented. The electromechanically coupled circuit equation excited by infinitely many vibration modes is derived. The governing electromechanical equations are reduced to ordinary differential equations in modal coordinates and eventually an infinite set of algebraic equations is obtained for the complex modal vibration response and the complex voltage response of the energy harvester beam. One single vibration mode is chosen and discussed. The periodic motions are obtained through an implicit mapping method with high accuracy, stability and bifurcations of periodic motions are determined by the eigenvalue analysis. Frequency-amplitude characteristics of periodic motions are achieved by the Fourier transform

京都大学 / 新制・課程博士 / 博士(情報学) / 甲第24737号 / 情博第825号 / 新制||情||138(附属図書館) / 京都大学大学院情報学研究科先端数理科学専攻 / (主査)教授 青柳 富誌生, 教授 田口 智清, 准教授 寺前 順之介 / 学位規則第4条第1項該当 / Doctor of Informatics / Kyoto University / DFAM

No description available.

京都大学 / 新制・課程博士 / 博士(情報学) / 甲第23587号 / 情博第781号 / 新制||情||133(附属図書館) / 京都大学大学院情報学研究科数理工学専攻 / (主査)教授 矢ヶ崎 一幸, 教授 梅野 健, 准教授 柴山 允瑠 / 学位規則第4条第1項該当 / Doctor of Informatics / Kyoto University / DFAM

Pages 10, 46, 126, 142 and 146 have been omitted because they were completely blank. / <p> This thesis describes the development of a tunable, ultrashort-pulse semiconductor-based laser system operating in the 1 μm wavelength region. The design of the oscillator is based on a two-contact long-wavelength InGaAs-GaAs quantum-well semiconductor device containing integrated gain and saturable absorber sections. A key design component of the oscillator is the fabrication of a curved ridge-waveguide in the gain section of the device, which allows the laser to be operated in a compact, linear external cavity. Under conditions of passive or hybrid mode-locking, the semiconductor oscillator can generate pulses of 1 to 10 ps in duration, which are tunable from 1030 to 1090 nm. The oscillator is also capable of being passively mode-locked at harmonics of the cavity round-trip frequency, allowing tuning of the pulse repetition rate from 0.5 to over 5 GHz. Noise measurements on two independently hybridly mode-locked semiconductor lasers reveal that the absolute noise of each laser is dominated by phase noise at frequencies below 10^5 Hz, while amplitude noise dominates at higher frequencies.</p> <p>Semiconductor and fibre optical amplifiers are used to scale the average power level of the mode-locked pulses. Semiconductor optical amplifiers consisting of narrow-stripe and flared-waveguide designs have been fabricated using the same material structure as that of the mode-locked semiconductor oscillator. Narrow-stripe devices with a length of 800 μm have produced amplified average signal powers of 13 mW, while 1700-μm-long, 2° flared-waveguide devices have produced amplified average signal powers of 50 mW. A fibre-based system consisting of a single-mode double-clad Yb-doped fibre has been constructed to investigate the suitability of a mode-locked diode laser as a seed-source for a Yb:fibre amplifier. Amplified average signal powers of up to 1.4 W have been obtained at the output of the fibre for a launched pump power of 2.1 W. Compression of the amplified pulses using a modified dual-grating compressor yields pulse durations as low as 500 fs and a peak power of up to 1.5 kW.</p> <p> Preliminary work is reported on the development of a novel dual-wavelength optical source consisting of two synchronized mode-locked diode lasers and a polarization-maintaining Yb:fibre amplifier. Numerical simulations based on a rate-equation model for the amplifier gain are conducted to investigate the performance characteristics of a Yb:fibre amplifier when operated under dual-wavelength signal amplification. The simulations are used to predict and optimize the performance of the fibre amplifier for two mode-locked semiconductor-seed-oscillators operating at wavelengths of 1040 and 1079 nm. Good agreement is obtained between the simulations and experimental results. </p> / Thesis / Doctor of Philosophy (PhD)

This thesis is principally concerned with the conditions under which a feedback oscillator with a single non-linear element can support two component waves, These component waves are required to have unrelated frequencies. A theory is produced to predict the oscillation frequencies and amplitudes and examine their stability. The conclusions reached in this thesis are then compared with those reached by previous workers in the same field. The concluding parts of the thesis contain an examination of the possible approximations which can be made in order to represent various non-linear elements mathematically and also a demonstration of a system for examining frequency relationships without recourse to direct numerical measurement. / Thesis / Master of Engineering (ME)

<p> The frequency pulling of the van dcr Pol nonlinear oscillator due to an external forcing signal is investigated. The nonlinearity is of the zero-memory symmetric-cut-off type following a cube law.</p> <p> An experimental oscillator was built, and curves of the frequency shift of the oscillator fundamental against the magnitude of the input forcing signal are shown, both for a sinusoidal input and for a narrow band noise input. An empirical result is derived.</p> <p> The case of the sinusoidal input is examined theoretically. The importance of harmonic and intermodulation frequencies in the oscillator output is shown, and relations giving the oscillator frequency shift are given for small forcing amplitudes and for large amplitudes when the oscillator is nearly synchronized.</p> / Thesis / Master of Engineering (MEngr)

The objective and motivation for this project is to design a low-power, low-noise oven-control circuit to optimize the stability of a MEMS oscillator. MEMS oscillators can be fabricated using conventional semiconductor manufacturing methods and can often be assembled in packages smaller than those of traditional crystal oscillators. However, one of their largest disadvantages currently is their high temperature coefficient of frequency (TCF), causing MEMS oscillators to be especially sensitive to temperature changes. Hence, this project focuses on designing a printed circuit board that will allow the user to manually tune a current passing through a resonator wire-bonded to the board to elevate the resonator temperature. This will ensure that the device's resonance frequency stays largely constant and that the oscillator provides a very stable signal.